<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8">
		<title></title>
		<style type="text/css">
			.father {
				display: flex;
				align-items: center;
				justify-content: center;
				height: 600px;
				background: purple;
			}

			.son {
				height: 200px;
				width: 200px;
				background: red;
			}
		</style>
	</head>
	<body>
		<div class="father">
			<div class="son">

			</div>
		</div>
	</body>
	<script>
	console.log(typeof(null))
	console.log(typeof(undefined))
	</script>
</html>
